The present invention relates to a composite piezoelectric transducer used for an ultrasonic probe and the like, particularly to a composite piezoelectric transducer having a resonance frequency distribution in plane, and to a method of fabricating the composite piezoelectric transducer. The present invention also relates to an ultrasonic probe and an ultrasonic examination device which employ the composite piezoelectric transducer and in which aperture control can be performed in a minor axis direction.
Japanese Laid-Open Patent Publication No.7-107595, for example, describes a known and conventional ultrasonic probe which can perform aperture control in a minor axis direction of the ultrasonic probe, and which has resonance frequency characteristics in a wide frequency band.
A conventional ultrasonic probe 100 shown in FIG. 16 is provided with a piezoelectric element 101 of which the thickness varies along the X direction. A matching layer 102 is disposed on an ultrasonic emitting face of the piezoelectric element 101. A large number of piezoelectric transducers each constituted by the piezoelectric element 101 and the matching layer 102 are arranged along the Y direction, and supported by a back-face load member 103.
In each of the piezoelectric elements 101, the thickness is the minimum in a center portion along the X direction, and the thickness is increased as getting closer to both ends. With piezoelectric elements having such a configuration, it is possible to transmit and receive ultrasonic waves of higher frequencies in a center portion in the X direction of the piezoelectric transducer. In a peripheral portion, it is possible to transmit and receive ultrasonic waves of lower frequencies. As a result, the resonance frequency characteristics of the ultrasonic piezoelectric transducer are realized in a wider frequency band.
In the ultrasonic piezoelectric transducer shown in FIG. 16, an aperture size in the X direction is smaller with respect to the ultrasonic waves of higher frequencies, but is wider with respect to the ultrasonic waves of lower frequencies. Accordingly, it is possible to form a narrow ultrasonic beam from a short range to a long range, so that high resolution can be attained from a short range to a long range.
In the conventional ultrasonic probe shown in FIG. 16, however, the surface of the piezoelectric element is required to be worked so as to have a concave shape. In addition, it is necessary to form a matching layer having different curvatures in the concave face of the piezoelectric element. The production of such an ultrasonic probe is very difficult, or even if such an ultrasonic probe can be produced, the production is at variance with the reality in terms of the production yield and cost.